LAWRENCE, Mass. -- Investigators worked Friday to pinpoint the cause of a series of fiery natural gas explosions that killed a teen driver in his car just hours after he got his license, injured at least 25 others and left dozens of homes in smouldering ruins.

Authorities said an estimated 8,000 people were displaced at the height of Thursday's post-explosion chaos in three towns north of Boston rocked by the disaster. Most were still waiting, shaken and exhausted, to be allowed to return to their homes.

Gov. Charlie Baker said Friday that hundreds of gas technicians were being deployed throughout the night and into Saturday to make sure each home is safe to enter.

Even after residents return and their electricity is restored, gas service won't be turned on until technicians can inspect every connection in each home -- a process that could take weeks.

"This remains a tremendous inconvenience for many people," Baker said. "It's essential for the crews to get this right."

The National Transportation Safety Board sent a team to help investigate the blasts in a state where some of the aging gas pipeline system dates to the 1860s.

The rapid-fire series of gas explosions that one official described as "Armageddon" ignited fires in 60 to 80 homes in the working-class towns of Lawrence, Andover and North Andover, forcing entire neighbourhoods to evacuate as crews scrambled to fight the flames and shut off the gas and electricity.

Gas and electricity remained shut down Friday in most of the area, and entire neighbourhoods were eerily deserted.

Authorities said Leonel Rondon, 18, of Lawrence, died after a chimney toppled by an exploding house crashed into his car. He was rushed to a Boston hospital and pronounced dead Thursday evening.

Rondon, a musician who went by the name DJ Blaze, had just gotten his driver's license hours earlier, grieving friends and relatives told The Boston Globe. "It's crazy how this happened," said a friend, Cassandra Carrion.

The state Registry of Motor Vehicles said Rondon had been issued his driver's license only hours earlier Thursday.

The NTSB said Friday that its team should on the scene for a week. The agency said the team will be gathering perishable evidence from the accident site and pulling together information from federal, state, and local agencies, and from Columbia Gas.

The agency said among the issues to be examined are the design of the pipeline system, any upgrades and the operator's management of the pipeline. A review of the emergency response of the operator and local first responders will also be conducted.

Massachusetts State Police urged all residents with homes serviced by Columbia Gas in the three communities to evacuate, snarling traffic and causing widespread confusion as residents and local officials struggled to understand what was happening. Some 400 people spent the night in shelters, and school was cancelled Friday as families waited to return to their homes.

The governor said state and local authorities were investigating but it could take days or weeks before they turn up answers. He declared a state of emergency for the affected area so the state could take over recovery efforts.

Baker authorized the utility Eversource to take management control over the effort to restore services.

The Massachusetts Emergency Management Agency blamed the fires on gas lines that had become over-pressurized but said investigators were still examining what happened.

Capturing the mounting sense of frustration, Democratic U.S. Rep. Seth Moulton tweeted that he had called the utility's president several times with no response. "Everyone wants answers. And we deserve them," Moulton said.

Columbia Gas President Steve Bryant wouldn't comment on the suspected cause of the blasts, deflecting questions about his company's response but saying it had "substantive, lengthy conversations" with the authorities.

The Massachusetts gas pipeline system is among the oldest in the country, as much as 157 years old in some places, according to the Conservation Law Foundation, an environmental advocacy group.

Columbia Gas had announced earlier Thursday that it would be upgrading gas lines in neighbourhoods across the state, including the area where the explosions happened. It was not clear whether work was happening there Thursday, and a spokeswoman did not return calls seeking comment.

U.S. Sens. Elizabeth Warren and Edward Markey said they are calling on the Senate's Commerce, Science and Transportation Committee to hold a hearing to determine what went wrong and how to make sure it doesn't happen again.

At least one story of heroism emerged from the ashes: that of Lawrence police officer Ivan Soto. His house burned nearly to the ground, but after rushing home to check on his family and warn his neighbours to evacuate, he went back on patrol.

"He actually stayed on duty even though his house was burning down" neighbour Christel Nazario told The Associated Press. "I don't know how he did it."

The three communities house more than 146,000 residents about 26 miles (40 kilometres) north of Boston, near the New Hampshire border. Lawrence, the largest, is a majority Latino city with a population of about 80,000.

Lawrence Mayor Dan Rivera reassured immigrants who might not be living in his city legally that they had nothing to fear.

"Do not be afraid. Stay in the light. We will support you and your family," Rivera said at a news conference Friday, speaking in English and Spanish. "Lawrence is one community."

Authorities said all of the fires had been extinguished overnight and the situation was stabilizing. But Rivera criticized the gas utility for poor communications and accused the company of "hiding from the problem."

On Thursday, Andover Fire Chief Michael Mansfield described the unfolding scene as "Armageddon."

"There were billows of smoke coming from Lawrence behind me. I could see pillars of smoke in front of me from the town of Andover," he told reporters.

Aerial footage of the area showed some homes that appeared to be torn apart by the blasts.

Brenda Charest stood anxiously on her front porch while a crew checked her undamaged home before giving her the all-clear to return Friday. On Thursday, she had come home to a hissing sound in her basement and a strong odour of natural gas.

"We took off. I said, 'Pack up, we're out of here,"' said Charest, who went with her 93-year old father and cat to a relative's home. "It was scary. We didn't know anything."

Columbia Gas was fined $100,000 by the state for a variety of safety violations since 2010, including $35,000 in 2016 for failing to follow company and pipeline safety regulations when responding to an outage and repairing a leak in Taunton.

The company was sued in 2014 after a strip club was destroyed in a natural gas explosion in Springfield, Massachusetts, after a Columbia employee accidentally punctured a gas line while probing for a leak. The November 2012 blast levelled the Scores Gentleman's Club, injuring about 20 people and damaging dozens of other buildings. The club owner and the gas company eventually settled the case.

Gas explosions have claimed lives and destroyed property around the U.S. in recent years.

In 2016, a buildup of natural gas triggered an explosion and fire that killed seven people in apartments in Silver Spring, Maryland.

In 2014, a gas explosion in New York City's East Harlem neighbourhood killed eight people and injured about 50. Consolidated Edison later agreed to pay $153 million to settle charges after the state's Public Service Commission found it had violated state safety regulations. A gas leak had been reported before that blast.

A 2011 natural gas explosion killed five people in Allentown, Pennsylvania, and that state's largest gas utility was fined by regulators, who called the company's safety record "downright alarming."

Photos

People walk with suitcases and belongings down South Broadway Street in South Lawrence, Mass., Friday, Sept. 14, 2018, after a massive natural gas disaster Friday that affected areas in Lawrence, Andover and North Andover, Mass. (Amanda Sabga/The Eagle-Tribune via AP)

In this image take from video provided by WCVB in Boston, firefighters battle a large structure fire in Lawrence, Mass, a suburb of Boston, Thursday, Sept. 13, 2018. Emergency crews are responding to what they believe is a series of gas explosions that have damaged homes across three communities north of Boston. (WCVB via AP)

Multiple fire trucks from surrounding communities arrive Thursday, Sept. 13, 2018, in Lawrence, Mass., responding to a series of gas explosions and fires triggered by a problem with a gas line that feeds homes in several communities north of Boston. (AP Photo/Phil Marcelo)